Powder X-ray phosphors, such as CaWO.sub.4, Gd.sub.2 O.sub.2 S:Tb, LaOBr:Tb, and BaFCl:Eu are known and used as X-ray intensifying screens in X-ray radiology, X-ray spectrometry, and X-ray radiography. Powder phosphors are not readily formable into complex shapes. Crystalline NaI:Tl and Bi.sub.4 Ge.sub.3 O.sub.12 (BGO) are used as the X-ray scintillator for scintillation counters. Crystalline and powdered crystalline phosphors are also difficult to form into complex shapes.
Vitreous or glassy phosphors, either in powder or glass form, would be desirable where X-ray phosphors are used. However, vitreous phosphors or glassy phosphors tend to have low X-ray to light conversion efficiencies when compared to the previously mentioned crystalline phosphors. The development of a vitreous or glassy phosphor with a higher light output would enable the formation of a transparent glass which is easily formable into any desired shape. The activator can be more evenly distributed in the glassy phosphor than in a crystalliine phosphor. Lower cost scintillators could be produced with a cast glass phosphor than with crystalline phosphors.
U.S. Pat. No. 4,038,203 discloses certain alkali metal-rare earth temperature ultra-violet photoluminescent glasses. The alkali photoluminescent glasses described in the patent are hydroscopic and have a tendency to crack during preparation. In addition, for the terbium-activated alkali metal-rare earth metaphosphate glasses of the patent, increasing the atomic weight of the alkali metal with a fixed n or increasing the n for a fixed alkali metal increases the intensity of the light emitted from the glass as reported at the May 1979 Electrochemical Society Meeting and in the Extended Abstracts, Vol. 79-1, Abstract No. 223, pp. 574-575.
Thus, it would be highly desirable to have a transparent glass which exhibits X-ray luminescence, does not crack or absorb water during preparation, can be cast or formed into shapes, and permits a more homogeneous incorporation of the activator into the composition than with a crystalline phosphor.